1. Field of the Invention
This invention relates to a knife roll for cutting windows out of window envelope blanks.
2. The Prior Art
Such a knife roll is known from U.S. Pat. No. 4,537,588, which shows a knife roll for cutting out the window in window letter envelopes. As the envelope blank is transported with the knife roll, the waste produced by cutting out the window must be retained for a certain time before discharge into a waste hopper. This is accomplished by an axially aligned, single row of suction apertures feeding near the roll surface enclosed by the foil knives. There is another axially extending row of suction apertures in the surface of the roll, which is connected with its own suction* air control channel in the carrier shaft.
However, the row of suction apertures is located in the direction of rotation of the knife roll in front of the knives, and temporarily retains the front edge of the envelope blank on the surface of the roll. Only one single window can be cut out with the cutting roll, and the waste can then be carried along by the knife (or cutting) roll to a discharge point following in the circumferential direction. Furthermore, only one defined size of blanks can be processed, where the spacing of the window from the front edge of the blank is within a comparatively narrow range.
U.S. Pat. No. 3,172,321 discloses a counter roll cooperating with a cutting roll for cutting out windows. The counter roll transports the letter envelope blanks to be provided with windows past the cutting roll. For this purpose, the counter roll has several axially extending rows of suction holes arranged one after the other, with each hole circumferentially spaced from each other. A vacuum can be selectively admitted to the suction holes via a carrier shaft with two axial control channels for suction air. Each channel is communicatively connected via substantially radial channels with an axial distribution channel in the circumferential surface of the carrier shaft. A cup-shaped ring sector having rows of suction holes is supported on the carrier shaft and can be rotated and fixed versus the carrier shaft so that two neighboring rows of holes can be selectively connected with distributing grooves and thus with the suction-air control channels.
However, the two rows of suction holes to which vacuum can be admitted exclusively retain the leading edge of the blank on the counter roll. Adjustments only permit adaptation to different formats (sizes) or spacings between the leading edge of the blank and the window to be cut out. This cutting does not occur near the rows of suction holes, but in a cutting sector following in the circumferential direction. The cutting sector has a particularly hard surface and no suction holes. Therefore, waste cannot be transported in a controlled manner and via vacuum action to a predetermined location for discard.
European Patent No. 0 436 142 shows a knife roller in which foil knifes are chucked on a part of the body of the roll. The roll has a multitude of suction holes arranged in rows on its circumference, for temporarily retaining the material cut out from a letter envelope blank. Suction air control disks arranged on the face side on this part of the roll body enable the periodic feeding of controlled suction air to defined rows of suction holes, via longitudinal boreholes in the axle of the roll. It is thus possible to precisely seize and discharge cut out material with displacement in the circumferential direction of the knife roll. The suction air control disks rotating synchronously with the knife roll are adjustable only relative to the part of the body of the roll, and only have a distribution function in order to admit suction air to selected rows of suction holes. It is a drawback of this reference that the controlled suction air has to travel a long distance, from a suction air control valve through the longitudinal boreholes and the suction air control disks to its site of application on the suction holes on the circumference of the knife roll. This highly impairs chronologically exact seizing and discharging of the pieces of material cut out at high speeds of the roll. Since at most only two suction air control disks can be employed with this knife roll, the number of rows of suction holes to which suction air can be admitted in a controlled way with any one adjustment is limited to two as well, and so is the number of pieces of material transported with one turn (or rotation) of the roll.
Furthermore, an additional suction strip is needed that requires its own support, its own supply of suction air and its own drive. Due to the spatially restricted arrangement of the suction strip and the cutting foil, it is not possible to place window cutouts near the end of the letter envelope blank seized by the suction strip.